1. Field of the Invention
The present invention relates to a height adjusting device for a vehicle seat which is adapted to adjust the height of the seat.
2. Description of Prior Art
In a vehicle seat, the height thereof is adjusted mechanically as desired according to the height of the occupant on the seat or what optimum eye level he or she wishes to set during driving of the vehicle, and for that purpose most of general seat adjusting devices are constructed such that the seat surface is to be moved vertically, keeping its horizontal line in parallel with the floor of the vehicle, utilizing a parallel linkage. Thus, in general, the seat frame is provided with a pair of forward link members and a pair of rearward link members, respectively, at its forward and rearward end parts, with those four link members being disposed in a parallel relation with one another.
In such parallel-linkage based seat height adjusting devices, however, a difficulty has been found its in terms of its seat surface inclination adjustment, because the seat surface has to be moved in a parallel way with respect to the floor of the vehicle. While some tilting mechanism can be installed therein, the problem is that such tilting mechanism needs to be equipped with the forward and rearward end part of the seat frame respectively so that, for example, to tilt the seat downwardly requires actuating one of the two tilting mechanisms and adjusting the other of them so as to leave it somewhat inactive, to thereby keep the parallel vertical movements of the seat.
A partial solution to such problem is found in the Japanese Laid-Open Utility Model Publication No. 56-28439 wherein there are disclosed a seat height adjusting means and a seat surface inclination adjusting means. However, according to this prior art, once the seat surface inclination has been adjusted, the seat height is not maintained in parallel with the floor of an automobile. In other words, the forward and rearward linkages between the seat frame and base bracket fixed to the floor are different in angle from each other, as a result of which the operation of the seat surface inclination adjusting means changes the inclination angle of the seat surface, which leaves its seat inclination angle to the seat height, and as such the seat surface inclination adjustment and parallel seat height adjustment can not be effected independently without their mutual co-active influences.